Ceramic matrix composites (CMC) have demonstrated utility as parts for turbines and other high temperature applications. CMC structures are most commonly constructed in the form of a two-dimensional (2D) laminate. A 2D laminate is constructed where two or more sheets of impregnated fibers, typically in the form of a woven cloth, are pressed together and heated to cure the matrix in and between the sheets. The life-limiting failure of such a structure is often due to delamination during repetitive thermal and mechanical cycling of the part due to shear failure in the matrix between fiber sheets. There is no cross-ply reinforcement in the 2D fiber architecture. Presently, most matrix materials delaminate under stress.
The mechanical reinforcement of a 2D laminate has been accomplished by the use of metallic fasteners placed through the sheets for the reinforcement of the laminate. Special bushings have been shown to compensate for the mismatch of thermal expansion characteristics of the ceramic and the metal placed through the sheets for the reinforcement. However, this approach is not always desirable. For many applications, the temperatures to which the metals are exposed are very high or the presence of the metal on both faces of the laminate is contradictory to the requirements for the article made from the composite. Nevertheless, in the absence of a matrix material of sufficient resistance to shear, mechanical reinforcement provides an attractive solution. A reinforcement that does not use a metal, or does not use a metal at a heat exposed surface, is desirable.
A ceramic matrix composite fastener has been disclosed in U.S. Pat. No. 6,042,315. The structure has a head and a shank such that the shank can be passed through a slot in a laminate panel. The head and slot are cut to have matching surfaces such that the panel can be attached to a housing. The fastener is constructed by a lay-up of fabric or tape where the fibers or tow are oriented at −45, 0, 45 and 90 degrees to yield a quasi-isotropic laminate. In this manner the stress on the head is partially carried by some fibers essentially aligned with the stress. Unfortunately, this is not necessarily the case with the panel where the stress is applied by the fastener perpendicular to the orientation of the fibers, resulting in the potential to promote the delamination of the panel.